Optical networking, including fiber-optics and optoelectronics, is an important aspect of high speed communication systems, particularly for its ability to allow for efficient, accurate, and rapid transmission of data between various components in the network system. As with most communication systems, the efficient use of space and power in optical networks is of ever-increasing importance. Further, design considerations for such networks must take into account the modularity of the particular components that are included in the network.
Indeed, modular components are desirable in fiber optic systems to reduce the cost of manufacturing the system, which increases as the system becomes more customized. This is at least one reason that silicon-on-insulator (SOI)-based optical components are becoming a preferred alternative, where optical elements such as lasers, photodiodes, active optical devices and passive optical devices are mounted on (or integrated within) the same SOI substrate as the associated optical waveguides. In some cases, the electrical integrated circuits (ICs) used to control the active optical devices are mounted on/integrated within a common SOI substrate with the optics.
An example of a modular component is an optical receiver module, which may also be a portion of a complete optical transceiver assembly (including both an optical transmitter module and an optical receiver module), or an optical transponder further comprising wavelength multiplexing/demultiplexing. A typical optical receiver module includes an input port/channel for an optical fiber (or other light propagating arrangement), a photodiode for detecting the incoming optical signals, and a sensing circuit for converting the optical signals to digital electrical signals compatible with other network components, with silicon-based optical waveguides used to interconnect these various components.
While such a modular component exhibits a significant improvement in reduced cost when compared to discrete element arrangements, a problem remains in that the silicon-based optical waveguides utilized in the modular are subject to polarization-dependent loss. That is, the propagation constants for the TE (transverse electric) and TM (transverse magnetic) modes of a silicon waveguide are different, and an optical signal of mixed polarization propagating along the waveguide will experience a greater degree of attenuation in one polarization mode with respect to the other.
To overcome this loss, polarization diversity optics are often employed to split an optical signal along two separate polarization-maintaining waveguides, with the TE mode signal retained along a first waveguide and the TM mode signal re-oriented along the second waveguide to align with the TE mode. Obviously, the need to introduce polarization diversity optics adds cost to the final assembly.
Thus, a need remains to reduce the polarization-dependent problems associated with the utilization of modular optical components.